The invention relates to a rotor for extracting energy from a flowing liquid, for example a tidal flow.
A flowing fluid possesses kinetic energy due to its motion. Naturally occurring fluid flows can be found in tidal currents, coastal or oceanic currents, river flows, thermal currents, air currents and elsewhere. Fluid flows can also be generated by man directly or indirectly. For instance, secondary fluid flows may be generated upstream or downstream of an obstacle placed in a naturally occurring fluid flow such as a dam in a river. Fluid flows may be generated by the transport of a fluid in a pipeline or by a machine such as fluid flows in a fluid system installed on a train, on a ship or on an automobile.
Energy conversion from gas flows such as air currents, i.e. wind-power, is a well developed technology. Numerous specially designed turbines have been made for extracting energy from the wind. However, the potential energy level is much larger in a liquid flow than in a gas flow because the fluid density is generally higher. For example, in tidal currents, fluid speeds in excess of 5 m/s may be generated, although a more typical speed may lie in the range of 1.5-2.5 m/s. Given that the density of seawater is around 1000 kg/m3, the energy density of tidal currents can typically be of the order of 4000 W/m2. In comparison, the density of air is around 1.2 kg/m3, therefore the energy density of wind at this speed is typically around 5 W/m2, this being around 800 times less than that available in a corresponding tidal current.
A need therefore exists for an improved device for extraction of energy from liquid flows such as tidal flows.